[amsat-bb] Full duplex handhelds for AO-85

Patrick STODDARD (WD9EWK/VA7EWK) amsat-bb at wd9ewk.net
Sat Oct 10 16:48:25 UTC 2015

Hi David!

I think that could be the case. Radios like these
Chinese-made HTs, and later versions of the Icom
IC-W32A sold over here (and possibly others - I
will try to dig up my Alinco DJ-G7T that is in a
box or bin in my garage), all of these suffer from
the same desense issues with the V/U satellites like
SO-50 and others. With the need to make Doppler
adjustments on the AO-85 uplink, along with slight
adjustments on the downlink to deal with the sharper
receive filtering in the Chinese-made radios, this
should open up more options for those wanting to work
this satellite full-duplex using a single radio.

Burns W2BFJ and I spent some time working the Fox-1A
engineering model's transponder last year at the
ARRL Centennial Convention. I had the KG-UV8D, Wouxun's
predecessor to the KG-UV9D I used last night, and
Burns had his Kenwood TH-D72A. I had the squelch wide
open on my radio, and moved the HT around while trying
to shield the HT's antenna, in an attempt to simulate
the downlink signals from this satellite in orbit. I
had an earpiece plugged into the KG-UV8D's speaker jack,
and Burns and I chatted as I walked around the
convention's main hall, and even a little ways outside
the hall. This is why I have had confidence that these
radios could handle full-duplex operation on this

Now we need to figure out how to be heard with the 5-watt
HTs through more of a pass, including the shallow passes...
hopefully the commissioning process will allow AMSAT to
make adjustments so this can happen.


Twitter: @WD9EWK

On Sat, Oct 10, 2015 at 1:08 PM, David G0MRF <g0mrf at aol.com> wrote:

Hi Patrick
> Interesting observation about the Chinese handhelds being able to
> work full duplex on AO-85 (U/V)
> but not on SO-50 (V/U)
> I saw some testing figures for harmonic output which suggested some radios
> use a single low pass with a cut-off just above 70cm, but the
> 2m transmitter uses the same filter.
> This meant the 3rd harmonic from 2m was very high and fell in the 70cm
> band de-sensing the radio.
> What you have proved (hopefully) is that there are no outputs from the
> 70cm transmitter which interfere with the 2m receiver and that the receiver
> front end is not de-sensed when transmitting up to AO-85.
> Nice.....
> Thanks
> David

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